The present invention relates to electromagnetic transducers for information storage and retrieval systems, such as disk or tape drives.
Current commercially available disk drives employ magnetoresistive (MR) sensors for reading data, and store data in domains having magnetizations that are substantially parallel to concentric media tracks, the parallel magnetic storage sometimes called longitudinal recording. It has been predicted that such longitudinal magnetic storage will become unstable at normal operating conditions when the domains reach a minimal size, termed the superparamagnetic limit. In order to store the data at higher density, the drive system may instead be designed to store data in domains that are substantially perpendicular to the disk surface, which may be termed perpendicular recording.
FIG. 9 shows a prior art system for perpendicular recording, which includes an inductive transducer 20 positioned in close proximity to a surface 25 of a medium such as a disk 22. The inductive transducer 20 has a U-shaped core 30 formed of high-permeability, low-coercivity or “soft magnetic” material and the disk 22 has a soft magnetic underlayer 33, the core and underlayer forming a magnetic circuit indicated by flux lines 28 that traverse a higher coercivity media layer 32, for magnetizing the media layer or reading the magnetization of the media layer. The core has magnetic pole tips 36 and 38 that differ in media-facing area so that the magnetic signal is concentrated in the smaller pole tip 36 for reading or writing data. The local portion of the disk may be travelling in the direction of arrow 40 or in a reverse direction, to write magnetic signals on a track. The pole tips are sufficiently separated to encourage magnetic flux to travel through the media, instead of across a submicron nonmagnetic gap that is typically employed for longitudinal recording. The prior art transducer of FIG. 9 is sometimes called a probe head.
Pole tip 36, which may be termed a write pole tip, may have a track-width and track-length dimensions that are each less than one micron, so that the media-facing area of the write pole tip is less than one square micron. A write pole layer may extend much further from the pole tip than it does in either the track-width or track-length dimensions, and so may sometimes be termed a probe layer. Such probe layers may have a remnant magnetization and/or domain instability that can cause partial erasure of recorded tracks.
Improved perpendicular recording heads are disclosed in U.S. patent application Ser. No. 10/724,385 (K35R1832) and U.S. patent application Ser. No. 10/724,309 (K35R1883), which are incorporated herein by reference. In those applications, a deflection pole is located downstream of the write pole tip, so that the magnetic field from the write pole tip is deflected from perpendicular and is more efficient in rotating perpendicular bits in the media. The deflection pole tip may be separated from the write pole tip by a submicron nonmagnetic gap that extends from the pole tips by a distance that may be termed a throat height.
In an article entitled “Single-Pole/TMR Heads for 140-Gb/in2 Perpendicular Recording,” Nakamoto et al. teach that data erasure, which is observed as write instability in a repeated read-rite operation, can be suppressed by combining a low throat height and a pole that is laminated with nonmagnetic layers so that the magnetic layers are antiparallel.